     (fn
       []
       ;(set! re-com.box/debug true)
-      [h-box
+      [h-split
        ;; Outer-most box height must be 100% to fill the entrie client height.
        ;; This assumes that height of <body> is itself also set to 100%.
        ;; width does not need to be set.
        :height   "100%"
-       :gap      "60px"
-       :children [[scroller
-                   :size  "none"
-                   :v-scroll :auto
-                   :h-scroll :off
-                   :child [v-box
-                           :children [[re-com-title-box]
-                                      [left-side-nav-bar selected-tab-id on-select-tab]]]]
-                  [scroller
-                   :child [v-box
-                           :size  "auto"
-                           :children [(when-not (-> js/goog .-labs .-userAgent .-browser .isChrome) [browser-alert])
-                                      [(:panel (item-for-id @selected-tab-id tabs-definition))]]]]]])))    ;; the tab panel to show, for the selected tab
+       ;:gap      "60px"
+       :initial-split 15
+       :margin "0px"
+       :panel-1 [scroller
+                 ;:size  "none"
+                 :v-scroll :auto
+                 :h-scroll :off
+                 :child [v-box
+                         :size "1"
+                         :children [[re-com-title-box]
+                                    [left-side-nav-bar selected-tab-id on-select-tab]]]]
+       :panel-2 [scroller
+                 :child [v-box
+                         :size  "1"
+                         :children [(when-not (-> js/goog .-labs .-userAgent .-browser .isChrome) [browser-alert])
+                                    [right-side-nav selected-tab-id]]]]])))    ;; the tab panel to show, for the selected tab
 
 (defn ^:export mount-demo
   []

            is-major?  (= (:level tab) :major)
            has-panel? (some? (:panel tab))]
      [:div
       {:style {:width            "150px"
                :line-height      "1.3em"
                :padding-left     (if is-major? "24px" "32px")
                :padding-top      (when is-major? "6px")

                       :color       "#fefefe"}
               ]]])


(defn right-side-nav [selected-tab-id]
  [box
   ;:height "100%"
   :child ((:panel (item-for-id @selected-tab-id tabs-definition)))])

(defn browser-alert
  []
  [box
